privacy exposure reduction: local mirroring of CDN resources

js/mirrors.js

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+/*******************************************************************************
+
+    µBlock - a Chromium browser extension to block requests.
+    Copyright (C) 2014 Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+*/
+
+/* global chrome, YaMD5, µBlock */
+
+/******************************************************************************/
+
+// Low-level asset files manager
+
+µBlock.mirrors = (function() {
+
+/******************************************************************************/
+
+var exports = {
+    bytesInUse: 0,
+    hitCount: 0
+};
+
+/******************************************************************************/
+
+var nullFunc = function() {};
+
+var mirrorCandidates = {
+          'ajax.googleapis.com': /^ajax\.googleapis\.com\/ajax\/libs\//,
+         'fonts.googleapis.com': /^fonts\.googleapis\.com/,
+            'fonts.gstatic.com': /^fonts\.gstatic\.com/,
+         'cdnjs.cloudflare.com': /^cdnjs\.cloudflare\.com\/ajax\/libs\//,
+              'code.jquery.com': /^code\.jquery\.com/,
+                  's0.2mdn.net': /(2mdn\.net\/instream\/html5\/ima3\.js)/,
+         'connect.facebook.net': /(connect\.facebook\.net\/[^\/]+\/all\.js)/,
+    'www.googletagservices.com': /(www\.googletagservices\.com\/tag\/js\/gpt\.js)/
+};
+
+
+var magicId = 'rmwwgwkzcgfv';
+var bytesInUseMax = 20 * 1024 * 1024;
+var ttl = 30 * 24 * 60 * 60 * 1000;
+var metadataPersistTimer = null;
+
+var metadata = {
+    magicId: magicId,
+    urlKeyToHashMap: {}
+};
+
+// Hash to content map
+var hashToDataUrlMap = {};
+
+var loaded = false;
+
+/******************************************************************************/
+
+var MetadataEntry = function(hash) {
+    this.accessTime = Date.now();
+    this.hash = hash;
+};
+
+var ContentEntry = function(dataURL) {
+    this.createTime = Date.now();
+    this.dataURL = dataURL;
+};
+
+/******************************************************************************/
+
+var getTextFileFromURL = function(url, onLoad, onError) {
+    if ( typeof onLoad !== 'function' ) {
+        onLoad = nullFunc;
+    }
+    if ( typeof onError !== 'function' ) {
+        onError = onLoad;
+    }
+    var xhr = new XMLHttpRequest();
+    xhr.responseType = 'text';
+    xhr.timeout = 10000;
+    xhr.onload = onLoad;
+    xhr.onerror = onError;
+    xhr.ontimeout = onError;
+    xhr.open('get', url, true);
+    xhr.send();
+};
+
+/******************************************************************************/
+
+// Extract a `key` from a URL.
+
+var toUrlKey = function(url) {
+    if ( url.slice(0, 4) !== 'http' ) {
+        return '';
+    }
+    var pos = url.indexOf('://');
+    if ( pos === -1 ) {
+        return '';
+    }
+    url = url.slice(pos + 3);
+    pos = url.indexOf('/');
+    if ( pos === -1 ) {
+        return -1;
+    }
+    var re = mirrorCandidates[url.slice(0, pos)];
+    if ( typeof re !== 'object' || typeof re.test !== 'function' ) {
+        return '';
+    }
+    var matches = re.exec(url);
+    if ( matches === null ) {
+        return '';
+    }
+    return matches.length === 1 ? url : matches[1];
+};
+
+/******************************************************************************/
+
+// Ref: http://www.iana.org/assignments/media-types/media-types.xhtml
+
+var normalizeContentType = function(ctin) {
+    var ctout;
+    var encoding;
+    var pos = ctin.indexOf(';');
+    if ( pos === -1 ) {
+        ctout = ctin.trim();
+        encoding = '';
+    } else {
+        ctout = ctin.slice(0, pos).trim();
+        encoding = ctin.slice(pos + 1).trim();
+    }
+    if ( encoding !== '' ) {
+        ctout += ';' + encoding;
+    }
+    return ctout;
+};
+
+/******************************************************************************/
+
+var metadataExists = function(urlKey) {
+    return typeof urlKey === 'string' && metadata.urlKeyToHashMap.hasOwnProperty(urlKey);
+};
+
+/******************************************************************************/
+
+var contentExists = function(hash) {
+    return typeof hash === 'string' && hashToDataUrlMap.hasOwnProperty(hash);
+};
+
+/******************************************************************************/
+
+var updateMetadata = function() {
+    metadataPersistTimer = null;
+    chrome.storage.local.set({ 'mirrors_metadata': metadata });
+};
+
+/******************************************************************************/
+
+var updateMetadataAsync = function(urlKey, hash) {
+    var doesExist = metadataExists(urlKey);
+    if ( doesExist ) {
+        metadata.urlKeyToHashMap[urlKey].accessTime = Date.now();
+        if ( metadataPersistTimer === null ) {
+            setTimeout(updateMetadata, 60 * 1000);
+        }
+        return;
+    }
+    metadata.urlKeyToHashMap[urlKey] = new MetadataEntry(hash);
+    if ( metadataPersistTimer !== null ) {
+        clearTimeout(metadataPersistTimer);
+    }
+    updateMetadata();
+};
+
+/******************************************************************************/
+
+var updateContent = function(hash, dataURL) {
+    if ( contentExists(hash) !== false ) {
+        return;
+    }
+    var contentEntry = hashToDataUrlMap[hash] = new ContentEntry(dataURL);
+    exports.bytesInUse += dataURL.length;
+    var key = 'mirrors_item_' + hash;
+    var bin = {};
+    bin[key] = contentEntry;
+    chrome.storage.local.set(bin);
+};
+
+/******************************************************************************/
+
+var cacheAsset = function(url) {
+    var urlKey = toUrlKey(url);
+    if ( metadataExists(urlKey) ) {
+        return;
+    }
+
+    var onRemoteAssetLoaded = function() {
+        this.onload = this.onerror = null;
+        if ( this.status !== 200 ) {
+            return;
+        }
+        var contentType = normalizeContentType(this.getResponseHeader('Content-Type'));
+        if ( contentType === '' ) {
+            //console.debug('mirrors.cacheAsset(): no good content type available');
+            return;
+        }
+        var yamd5 = new YaMD5();
+        yamd5.appendAsciiStr(contentType);
+        yamd5.appendAsciiStr(this.response);
+        var hash = yamd5.end();
+        updateMetadataAsync(urlKey, hash);
+        if ( contentExists(hash) ) {
+            //console.debug('mirrors.cacheAsset(): reusing existing content for "%s"', urlKey);
+            return;
+        }
+        //console.debug('mirrors.cacheAsset(): caching new content for "%s"', urlKey);
+        // Keep original encoding if there was one, otherwise use base64 --
+        // as the result is somewhat more compact I believe
+        var dataUrl = contentType.indexOf(';') !== -1 ?
+            'data:' + contentType + ',' + encodeURIComponent(this.responseText) :
+            'data:' + contentType + ';base64,' + btoa(this.response);
+        updateContent(hash, dataUrl);
+    };
+
+    var onRemoteAssetError = function() {
+        this.onload = this.onerror = null;
+    };
+
+    getTextFileFromURL(
+        url,
+        onRemoteAssetLoaded,
+        onRemoteAssetError
+    );
+};
+
+/******************************************************************************/
+
+var toURL = function(url, cache) {
+    var urlKey = toUrlKey(url);
+    if ( urlKey === '' ) {
+        return '';
+    }
+    if ( metadataExists(urlKey) === false ) {
+        if ( cache === true ) {
+            cacheAsset(url);
+        }
+        return '';
+    }
+    var metadataEntry = metadata.urlKeyToHashMap[urlKey];
+    if ( contentExists(metadataEntry.hash) === false ) {
+        return '';
+    }
+    var contentEntry = hashToDataUrlMap[metadataEntry.hash];
+    updateMetadataAsync(urlKey);
+    exports.hitCount += 1;
+    return contentEntry.dataURL;
+};
+
+/******************************************************************************/
+
+var load = function() {
+    loaded = true;
+
+    var loadContent = function(hash) {
+        var key = 'mirrors_item_' + hash;
+        var onContentReady = function(bin) {
+            if ( chrome.runtime.lastError ) {
+                return;
+            }
+            var contentEntry = bin[key];
+            hashToDataUrlMap[hash] = contentEntry;
+            exports.bytesInUse += contentEntry.dataURL.length;
+        };
+        var bin = {};
+        bin[key] = '';
+        chrome.storage.local.get(bin, onContentReady);
+    };
+
+    var onMetadataReady = function(bin) {
+        if ( chrome.runtime.lastError ) {
+            return;
+        }
+        metadata = bin.mirrors_metadata;
+        var hemap = metadata.urlKeyToHashMap;
+        for ( var urlKey in hemap ) {
+            if ( hemap.hasOwnProperty(urlKey) === false ) {
+                continue;
+            }
+            loadContent(hemap[urlKey].hash);
+        }
+    };
+
+    chrome.storage.local.get({ 'mirrors_metadata' : metadata }, onMetadataReady);
+};
+
+/******************************************************************************/
+
+var unload = function() {
+    if ( metadataPersistTimer !== null ) {
+        updateMetadata();
+    }
+    metadata.urlKeyToHashMap = {};
+    hashToDataUrlMap = {};
+    exports.bytesInUse = 0;
+    exports.hitCount = 0;
+
+    loaded = false;
+};
+
+/******************************************************************************/
+
+exports.toggle = function(on) {
+    if ( on && loaded !== true ) {
+        load();
+    } else if ( on !== true && loaded ) {
+        unload();
+    }
+};
+
+/******************************************************************************/
+
+// Export API
+
+exports.toURL = toURL;
+
+return exports;
+
+/******************************************************************************/
+
+})();
+
+/******************************************************************************/